This device relates to an improvement in the generation of carbon dioxide, and more particularly to a self-sustaining, on-site generation of carbon dioxide.
Commercial carbon dioxide is widely used and is generally manufactured by separation and purification from carbon-dioxide-rich gases produced by combustion or by biological processes. It is also found in underground formations in some states. Carbon dioxide is also commercially available as high-pressure cylinder gas [about 300 psig], in refrigerated liquid form, or as a solid [dry ice].
Common uses of carbon dioxide include, among other uses, use in fire extinguishing systems, for carbonation of soft drinks and beer, freezing of food products, refrigeration and maintenance of environmental conditions during transportation of food products, enhancement of oil recovery from wells, materials production [such as plastics and rubber], and treatment of alkaline water, as a shield during welding where it protects the weld against oxidation, dry ice pellets for sand blasting surfaces without leaving residues, in the chemical processing industry such as methanol production, for priming oil wells to maintain pressure in the oil formation, for removing flash from rubber or plastic objects by tumbling with dry ice, for the creation of inert blankets or environments, for the prevention of fungal and bacterial growth, as an additive to oxygen for medical use, as a propellant in aerosol cans, and to aid in maintaining a level of 1000 ppm in green houses to increase production yields of vegetables and flowers, to name a few.
To meet the needs of these various applications, requiring from small quantities of carbon dioxide (less than a pound/day) to extremely large quantities (tons/day), carbon dioxide is available as a compressed gas requiring heavy cylinders, or a liquid under pressure available from tube or liquid trailers, or as solid dry ice.
Very small users rely on high pressure cylinders. Their distribution is generally conducted by locally-focused businesses that buy the gas in bulk liquid form and package it at their facilities. Small to medium size customers truck-in bulk liquid products that are then processed through evaporation to produce the gas. Larger customers' needs are often met with “tube trailers”, i.e., bundles of high-pressure cylinders mounted on wheeled platforms. Onsite” plants are usually installed by customers consuming more than 10 tons/day of the gas.
There is an increasing interest in user-owned, small, non-cryogenic gas generators, in many markets. Such generators are available for oxygen, hydrogen and nitrogen, but not for carbon dioxide. For example, small to medium size users of oxygen or nitrogen may find an economical supply alternative in pressure-swing-adsorption (PSA) plants. Or again, hydrogen and oxygen may be produced through electrolysis of water. High purity hydrogen may then be produced by purification of the stream by using palladium foil diffusers.
To-date, “on-site” economical carbon dioxide generators, such as are available for hydrogen and oxygen, do not exist, although the demand for carbon dioxide is substantial. Moreover, the benefits of these “on-site” generators are multiple. For example, generation on demand, as needed independence from suppliers and possible supply interruptions, cost-insensitivity to supply issues no need for pressure vessels, their storage and recycling, and the like.
To meet this need, applicant has invented an electrolytic process and methods to produce carbon dioxide from organic acids which were originally described in U.S. Pat. Nos. 6,780,304 and 6,387,228. Applicant has pursued the development of that generation technology by developing multiple electrochemical cells assembled in stacks to achieve production rates and volumes much larger than those described in these patents.
Continuing in this vein, applicant has now designed an entire, self-sufficient carbon dioxide generation system comprised of solar panels, an electronic control unit for the transfer of solar energy to a battery, an electronic control module controlling the current output to an electrochemical carbon dioxide generator [electrolyzer] such as disclosed in applicant's pending application, application Ser. No. 11/650,016 filed on Jan. 5, 2007, which is hereby incorporated by reference.
The preferred mode utilizes the carbon dioxide generator disclosed in applicant's pending application ['016] which comprises a stack of at least two electrochemical cells, though any on-site carbon dioxide generator suited for the intended purpose may be used. The targeted carbon dioxide generation rate was 12 Liters/hour (0.05 lb/hr) for a duration of 10 hours per day, however, the system has been designed to, and can, generate in excess of 45 L/hr (0.18 lb/hr).
To create the self-sufficient carbon dioxide generation system applicant first devised a novel process to produce solid oxalic acid [OA] toroidal “briquets” weighing about 2 kg. each for placement and use in the novel dispenser. This generation and dispensing device designed by applicant forms the primary subject matter of this current application. Assembling and placing four such toroidal briquets into the device would allow for autonomous system operation and carbon dioxide generation for about one month, provided adequate solar energy can be harvested to sustain operation.
These oxalic acid [OA] toroidal briquets are used as the source for carbon dioxide generation. Anhydrous OA contains as much as 97.7 wt % carbon dioxide and therefore is the preferred source though, in some instances, oxalic acid dihydrate [OA 2H2O] can also be used. As developed by applicant, each toroidal briquet has an external diameter of approximately 25 cm, an internal diameter of approximately 10 cm, a thickness of approximately 3.5 cm, and weighs approximately 2.1 kg. A single toroidal briquet is adequate to support operation, at the nominal 12L/hr rate, for up to 9 days. As many as four such toroidal briquets can be stacked up in applicant's generating and dispensing device.
It should be understood that the size and dimensions of the toroidal briquet can vary as can the dimensions of the generating and dispensing device to accommodate the varying sizes of the toroidal briquet.
The toroidal briquets are compact, solid OA that can be easily handled without undue precaution. The ability to stack these toroidal briquets is the key component of the sub-system which makes the generating and dispensing device the vital and indispensable component thereof. The generating and dispensing device has an inner chamber inside of which the carbon dioxide generator of my pending application ['615], one or more, may be housed and outside of which the toroidal briquets are stacked. An upstanding inner cylindrical wall [central pipe] extending from the floor of the generating and dispensing device up to approximately its top form a barrier between the carbon dioxide generator and the toroidal briquets. With current applied to the carbon dioxide generator and the desired carbon dioxide generation rate is set, the system will generate carbon dioxide without any human oversight, interface, or maintenance.
Through experimentation is has been shown that the system is capable of producing approximately 9.12 L/hr of carbon dioxide per amp. A current load of approximately 1.32 amps has been shown to be adequate to achieve the nominal carbon dioxide generation rate. A current load of approximately 3.29 amps has proven to be adequate to generate approximately 30 L carbon dioxide/hr.
Under these current loads the voltage applied to an electrolyzer, for example, holding 10 electrochemical cells, in series connection, is approximately 12 volts. Consequently, a 12-volt battery should be adequate for the entire system for adequate operation and uninterrupted and unsupervised carbon dioxide generation. The nominal power requirement should be between approximately 16 watts to approximately 40 watts for a maximum rate of production of approximately 30 L/hr of carbon dioxide. With the system operating for approximately 10 hours/day, the total daily energy required will be approximately 160 to 400 watt-hours.
The container of the generating and dispensing device is approximately 30 cm in diameter and approximately 16 cm high. The upstanding inner cylindrical wall [or central pipe] has a diameter which is smaller than the diameter of the inner diameter of the toroidal briquet. Given this configuration it can been seen that up to four toroidal briquets can be staked into the container. A lid is securely attached to the container. It has through holes for the stack terminals and the exhaust gas. The thick-walled container has been especially molded for this application. The toroidal briquets are to be located between the outer wall of the container and its upstanding inner cylindrical wall. As previously mentioned, this upstanding inner cylindrical wall is attached to the floor of the container and prevents the OA toroidal briquets from interfering with the extraction of the stack of toroidal briquets, should maintenance be required.
Before operation approximately 1-2 pints of water are poured into the container to initiate the process to dissolve the bottom most OA toroidal briquet.
The system has been designed to operate during night-time hours. Therefore any solar-generated energy is to be stored for nighttime consumption. The battery described above is selected on the basis of its ability to store sufficient energy for 1-2 days of operation during cloudy days. The battery voltage is selected for its compatibility with solar panels and the current load required by the electrolyzer [carbon dioxide generator]. As noted above a 12-volt, 55 A-hr battery is adequate for the nominal generation rate. The battery selected is a 490T SunXtender. A larger battery such as a 560T or 690T model with storage capacity of 63 and 79 A-hr will be needed for the sustained operation at 30 L/hr.
Two control units are necessary to the operation of the system as described; a conventional commercially-available charge controller and a commercially-available modified load current controller. A typical charge controller, such as a Steca PR 110 unit is suitable for the intended purpose. Its main function is the regulation of current and voltage between panels and the battery to optimize battery charging without overload, and the like.
The load controller developed as part of this project provides current regulation from the battery to the electrolyzer [carbon dioxide generator]. The unit design is based on Linear Technology model LTC3780 Buck-Boost Controller, configured as a constant current source. The circuitry provides for efficient power conversion from battery to load while operating over a wide range of input voltages and load impedances. Presently the efficiency of either controller is estimated at approximately 90%. For energy efficient systems this could be increased by careful selection of certain components.
The primary source of energy contemplated is solar energy which is collected during the daytime and stored into a conventional commercially-available rechargeable battery. Surplus solar energy is dumped when the battery is fully charged. If adequate solar energy is not available, the load will extract energy mainly from the battery and progressively go dormant [the load current decreases] to protect the battery from deep discharge which would result in reduced life. The stability of the system will therefore depend on levels of insolation, battery capacity, and load demand.
During the months of interest for carbon dioxide use, and therefore generation [generally late Spring to early Fall] daytime exceeds 10 hours, insolation is high, and the conditions are optimum for the system. In the event of continuous cloud coverage for up to two days, the system is de-rated only producing partial carbon dioxide output. A daily operating duration of the generator of 10-12 hours is anticipated.
The generation rate can be selected manually by operation of a rotary switch at varying discrete values of 0, 12, 18, 24, and 30 L./hour. Once the rate is set, generation of carbon dioxide is quasi-instantaneous. The rates, however, can be changed at will.
During operation, toroidal briquet is dissolved and the saturated toroidal briquet solution is decomposed into carbon dioxide and hydrogen. The carbon dioxide gas evolves through the apertures in the inner wall [central pipe] and is released through the discharge vent located at the approximate center of the lid. The lid also can hold means to scrub the gas phase and/or means to hold a secondary releaser that will continuously feed a pheromone, such as octenol, into the exhaust stream as may be necessary or desired to attract insects.
The foregoing has outlined some of the more pertinent objects of the generating and dispensing device. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the generating and dispensing device. Many other beneficial results can be attained by applying the disclosed generating and dispensing device in a different manner or by modifying the generating and dispensing device within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the generating and dispensing device may be had by referring to the summary of the generating and dispensing device and the detailed description of the preferred embodiment in addition to the scope of the generating and dispensing device defined by the claims taken in conjunction with the accompanying drawings.